1. Field of the Art
The present invention relates to a vacuum-type sewage collecting apparatus for collecting sewage from a plurality of houses or facilities. More particularly, the present invention relates to a vacuum-type sewage collecting apparatus wherein a structure for use in operating a vacuum valve is improved.
2. Prior Art
Hitherto, a vacuum-type sewage collecting apparatus for collecting sewage from a plurality of houses or facilities has been known.
FIG. 3 illustrates the overall structure of a vacuum-type sewage collecting apparatus of the type described above.
As shown in the drawing, sewage discharged from each house 30 on the ground passes through sewage pipes 5 disposed underground and is discharged into cesspools 4 disposed more deeply underground. When a predetermined quantity of sewage accumulates in the underground cesspool 4, a vacuum valve 3 provided in the upper portion of the inside of the cesspool 4 is opened so that sewage accumulated in the cesspool 4 is sucked through a suction pipe 11. The sewage sucked through the vacuum valve 3 via suction pipe 11 is introduced into a vacuum sewage pipe 1 arranged underground. Then, it is accumulated in an accumulating tank 10 in a vacuum pump plant 9. The sewage accumulated in the accumulating tank 10 is then sent to a sewage treatment plant or the like by a feeding pump 8.
A vacuum pump 7 is connected to the accumulating tank 10 to create negative pressure in the accumulating tank 10 and the vacuum sewage pipe 1.
FIG. 4 is a side elevational cross-sectional view of the vaccum valve 3 for use in a vacuum-type sewage accumulating apparatus of the type described above.
As shown in the drawing, the vacuum valve 3 is positioned between the vacuum sewage pipe 1 and the suction pipe 11 and is arranged in such a manner that a piston 3b thereof is usually pressed by a compression spring 3d so that a valve 3c integrated with the piston 3b is seated on a valve seat 3e. Thus, the portion between the vacuum sewage pipe 1 and the suction pipe 11 is closed to prevent sewage in the cesspool 4 from being sucked into the suction pipe 11.
When the quantity of sewage in the cesspool 4 reaches a predetermined level, it is detected by a sensor (not shown) and a detection signal is supplied to a vacuum valve controller 13. When the vacuum valve controller 13 receives the detection signal, a connecting pipe 2, connected at one end thereof to the controller, and a cylinder chamber 3a of the vacuum valve 3 are placed in communication with each other. Since the other end of the connecting pipe 2 is, as illustrated, in communication with the vacuum sewage pipe 1 disposed just downstream of the vacuum valve 3, the pressure in the cylinder chamber 3a is set at a negative level. As a result, the piston 3b is raised upwards so that the valve 3c is lifted from the valve seat 3e. Therefore, the vacuum sewage pipe 1 and the suction tube 11 communicate with each other.
Thus, the sewage in the cesspool 4 is, via the suction pipe 11, sucked into the vacuum sewage pipe 1, the pressure of which is at a negative level.
In the above-mentioned system, since a gas-liquid two-phase flow passes through the vacuum sewage pipe 1, the vacuum sewage pipe 1 is not filled with sewage during normal operation.
However, if the gas-liquid ratio is lowered for some reason or the quantity of sewage flowing through the system is considerably less at night, portions in the vacuum sewage pipe 1 arranged toward the vacuum pump plant 9 are filled with sewage, causing a so-called "air lock" to be generated. As a result, the vacuum pressure generated in the vacuum pump plant 9 may be considerably lowered at the peripheral positions of the system due to the several air locks formed in the pipe 1.
However, in the conventional system described above, the vacuum pressure for operating the vacuum valve 3 has been, as described above, taken from the portion of the vacuum sewage pipe 1 just downstream of the vacuum valve 3 which is positioned at substantially the same height as that of the vacuum valve 3. Therefore, if an air lock is formed in the pipe portion just downstream of the vacuum valve 3, the force generated to open the vacuum valve 3 becomes too weak. And, if the valve lifting force is insufficient to overcome the force of the compression spring 3d, it is impossible to completely open the valve 3c. Therefore, a problem arises in that the discharge of sewage cannot be efficiently performed.
If the valve 3c in insufficiently opened, it easily becomes clogged with waste matter causing the flow of sewage therethrough to be impeded.